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Diet could be a contributing factor. Do check out the
diet page and Suz’s site:
Feeding Your Joeys & Adult Gliders. Captive gliders have specialized dietary needs and need the proper blend of nutrients (with protein, fruits, veggies, vitamins, and calcium). You'll want to follow whatever diet you choose, as outlined. Don't mix and match the various plans or ingredients or you'll throw off the overall calcium to phosphorus (Ca:P) ratios, as well as introduce other unhealthy imbalances. A "ledbeater" type of mix could be included in several different diet plans. Tossing in fruits and veggies (or other food items) not included in the one diet you choose can be harmful.
Also, as others noted, the stress of being a single glider might be contributing to the hair loss. He already showed signs of it while at the pet store, so he might be more prone to overgrooming. Here are a couple of SunCoast newsletter articles you might find helpful:
Does Suncoast Sugar Gliders Sell Single Sugar Gliders?Will a sugar glider die if left alone?Sugar gliders are social, colony critters, and really thrive while with a same-species companion. If not given enough attention, they can definitely get stressed out. And overgrooming is one sign.
Another possible cause of overgrooming, especially on a particular spot, might be parasites or something. If you haven't yet, it would be a good idea to take him to a
glider-knowledgeable vet for a wellness exam, especially since he came from a pet store and wasn't raised in the healthiest of environments.
I'm moving this to Health & Hygiene for more responses.
Good luck, and do keep us posted!